An increasingly popular type of ultrasound imaging system is the sector scan imaging system. These systems typically employ a source of focused sonic energy, such as various combinations of transducers and/or mirrors and/or lenses, which are electronically or mechanically caused to move the sonic energy penetration back and forth such that discrete pulse-echo scans all pass into and out of the body of the subject from a relatively small area, which often is just at the contact point with the patient, or slightly thereabove or therebelow. Hence, the composite image which is developed from a large number of these radially extending discrete pulse-echo scans is in the form of a sector of a circle, which broadens as a function of depth of the pulse-echo scan into the patient. Such systems have been found clearly advantageous for applications such as cardiac imaging, wherein high sonic impedance elements, such as the rib cage, severely restrict the space through which the imaging system may have access to irradiate the relevant portion of the patient's body. Utilization of the sector scan approach allows for application and withdrawal of the ultrasound pulse-echo signals from a narrow point, with the sector or fan shaped imaging field suitably enclosing the image field.
One difficulty which is inherent to displaying the sector scan image relates to the voids (also referred to herein as "holes" or "blanks") between the discrete radial scans, for which no actual pulse-echo imaging data has been developed. These voids are themselves sector shaped, narrow near the top, or narrowest portion of the sector image, and becoming progressively wider near the bottom portion of the image field. For example, it is possible that, in the lower extremities of a sector scan image, upwards of ten to twelve out of every fourteen horizontal picture elements may constitute voids, about which no actual pulse-echo scan data is available. Obviously, production and display of a useful and subjective pleasing image is impossible unless some data actually is displayed for each picture element, in the viewing field, including these voids or blanks.
It is an object of the present invention to provide methods and apparatus for generating simulated data to fill the voids or holes between radially extending discrete pulse-echo scans in a sector scan system.
Typical approaches to such data simulation involve replication of actual data from the previous scan. Replication is quite impractical as the number of holes gets larger, perhaps approaching nine to twelve picture elements.
It is accordingly an important object of the present invention to provide a void filling scheme wherein the simulated data is appropriately produced based not only on the actual data developed at either side of the void, but also based upon the portion of the sector in which the display picture element is located.
It is no less important object that the generation and provision of such simulated data occur at a rate which is not detrimental to the critically important real time character of sector scan systems.
It is a still further object to provide an approach which allows adequate flexibility for operation in various types of scanning systems, such that changes in the weighting allocations may be simply wrought to adapt a given system to function in accordance with various system and imaging constraints.